Do not mix blastmasters with other sonic weapons. They work at cross purposes.

A blastmaster is a very expensive gun, possibly the most expensive squad weapon in the game. In order to utilize it, you want the squad with it to sit still and fire on its Heavy setting. Paying 40 points for 2 S5 shots/turn is simply not worth the investment.

Sonic Blasters are Move&Fire weapons, they're best used to lay down fire as you move to where you need to be. A Doom Siren is a Move&Fire Template that needs you to close with your opponent to be effective. Neither of these work well when combined with a blastmaster that needs to sit still to be useful.